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Access Portal for Dental Informatics, Computerized Dentistry and Dental CAD/CAM

 

 

CADCAM Materials

 

 

It took more than one hundred and twenty years before the computer, invented in eighteen eighty by Jacquard, and the use of ceramics in dentistry, first applied by Land in eighteen eighty-six, were combined to create computerized dentistry. Until recently, aesthetics were the key reason for opting for ceramics. An added criterion has become the tissue-friendliness of metal-free ceramics. The public has made its preference for biocompatibility known. The arrival of zirconium oxide relegated to the past the paradigm that ceramics require a different preparation and modeling approach than metal-ceramics. One of the blessings of computerized dentistry is that it enabled the application of zirconium oxide. The introduction of this material in restorative and prosthetic dentistry is most likely the decisive step towards the use of full ceramics without limitation.


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Zirconia

 

With the exception of zirconium oxide, existing ceramics systems lack reliable potential for the various indications for bridges without size limitations. Zirconium oxide with its high strength and comparatively higher fracture toughness seems to buck this trend. With a three-point bending strength exceeding nine hundred mega-Pascals, zirconium oxide can be used in virtually every full ceramic prosthetic solution, including bridges, implant supra structures and root dowel pins. The fact that zirconium oxide has been used in the industrial production of root dowel pins since nineteen ninety reaffirms the belief that its high strength yields clinical durability. The high strength and toughness are the result of a material-specific crystal transformation, specifically from a tetragonal to a monocline crystal structure, which stops cracking at the source. The increase in volume resulting from this transformation inhibits cracking and increases strength by an order of magnitude. In a nineteen ninety-two publication, Garvy compared zirconium oxide with hardened steel. The similarities in material properties proved astounding. The bending strength, modulus of elasticity, thermal expansion coefficient and specific gravity of both materials are comparable. The fact that both materials can attribute their strength to the same martensitic transformation of crystal structure accompanied by a nearly identical volume increase makes the comparison even more striking. In addition, both materials are opaque to X-ray.

Due to its specific material properties, zirconium oxide ceramic, referred to by the abbreviation Y-TZP, has been used for quite some time in orthopaedics as part of hip joint implants. Previous attempts to extend its application to dentistry were thwarted by the fact that this material could not be processed using traditional methods used in dentistry. The arrival of computerized dentistry enables the economically prudent use of zirconium oxide in such elements as base structures such as copings and bridges and implant supra structures. Special requirements apply to dental materials implanted for longer than a period of thirty days. Several technical requirements include high strength, corrosion resistance and defect-free producability at a reasonable price. The primary requirement, however, is biocompatibility, which means that there should be no rejection response, infection or any other problem related to the introduction of material in tissue. In vitro testing of zirconium oxide has thus far elicited no unfavourable responses when combined with cells or tissues. Moreover, short and long-term in vivo testing indicate excellent biocompatibility. This is further substantiated by the results of various clinical trials extending over a period of more than eight years, each of which reveals no unfavourable tissue responses.

    Ever more stringent requirements are being placed on the aesthetics of teeth. Metals and porcelain are currently the materials of choice for crowns and bridges. The demand for full ceramic solutions, however, continues to grow. Consequently, industry and science are increasingly compelled to develop full ceramic systems. In introducing full ceramic restorations, such as base structures made of sintered ceramics, computerized dentistry plays a key role. When discussing aesthetics, we must not focus solely on natural colored porcelain inlays, onlays and veneers milled with the aid of a computer, but also the application of various layers of dental glass ceramic on base structures. To increase the aesthetics of zirconium oxide, a glass ceramic layer can be applied onto the structure’s surface. Research focuses primarily on the strength of the bond between the zirconium oxide and the glass ceramic and the strength of the entire structure in terms of the difference in thermal expansion coefficient. The application of glass on zirconium oxide is infrequently discussed in the scientific literature. The first aim is to gain a good overview of the functional properties of the glass ceramic-zirconium oxide system in terms of the thermal compatibility of the components, interface integrity, form stability of glass ceramic when used in ceramic shoulders, integrity of the glass ceramic in terms of porosity and in vitro testing of fatigue sensitivity and strength of restorations. These results can be used to assess the risks associated with the clinical application of this type of restoration.

    Due in part to the growing demand for aesthetic and biocompatible, metal-free restorations, this research is important to predict an evidence-based estimate of clinical reliability. This will make it possible to evaluate the values found using a mathematical analysis of the designed restoration model based on the finite elements method. A number of international evaluation standards find their use in testing the functional product requirements and validating the production method. These standards, however, do not always respond to questions which are key to long-term in situ performance. At the same time, one of the study aims is to generate more definitive conclusions regarding the guidelines for use in dental indications for this type of restoration. The study will also address how the restoration is produced to determine which parameters are essential for the resulting quality of the restoration. The final aim is to improve the quality of the crown or prosthetic elements.